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PubMed2006

Verification of results to improve the quality of analytical data: a proposal.

After some two decades insisting on validation and normalization of methods, the reliability of the results in analytical chemistry continues to be unsatisfactory. Further, the processes involved are too slow, with the effect that frequently the most relevant results are obtained with methods not (yet) validated according to norms. It is time to rethink about how the reliability of the results could be improved. It is proposed to shift some of the control from the validation and normalization of method to the verification of the results, using verification tools built into the procedure: additional standards may enable the calculation of the yield of an extraction or chemical transformation, control the column performance or ensure that the fraction from a preseparation is correctly cut. Such verification tools provide control for every sample. If the correctness of results is verified for every sample, this confirms the adequate performance of the method and could replace a corresponding part of the validation. Examples are shown for a number of methods.

Chromatography↗
PubMed1997

Graphical interpretation of analytical data from comparison of a field method with reference method by use of difference plots.

Various viewpoints have been offered regarding the appropriate use of scatter plots or difference plots (bias plots or residual plots) in comparing analytical methods. In many of these discussions it seems the basic concepts of identity (within inherent imprecision) and acceptability based on analytical goals (analytical quality specifications) have been forgotten. With the increasing number of Reference Methods in laboratory medicine, these basic concepts are becoming more important in validation of field methods. Here we describe a simple and effective graphical test of these hypotheses (identity and acceptability) by use of difference plots. These plots display the underlying hypothesis before the measured differences are plotted and allow interpretation of the results according to specific criteria. We further describe simple but effective interpretations of the data, when the hypothesis is not fulfilled, by using two data sets drawn from comparisons of field methods for S-creatinine with a Reference Method for this analyte. The difference plot is a graphical tool with related simple statistics for comparison of a field method with a Reference Method, focusing on (a) identity within the inherent analytical imprecision or (b) acceptability within analytical quality specifications. Calculation of the standard deviation of the differences is an indispensable tool for evaluation of aberrant-sample bias (matrix effects).

Chemistry, Clinical↗
PubMed1996

Evaluation of multicomponent fluorimetric analytical data by use of partial least-squares calibration. Application to the determination of codeine and ephedrine in urine.

A partial least-squares calibration (PLS) method for the simultaneous spectrofluorimetric determination of acetylsalicylic acid, codeine and ephedrine is proposed. The use of PLS for the multicomponent spectrofluorimetric determination is demonstrated by analysing synthetic mixtures. Analyte mixtures can be resolved even in the presence of strongly overlapped fluorescence signals. The method was validated by subjecting experimental data to exhaustive statistical analysis. The proposed method was applied to the simultaneous determination of the three drugs in synthetic mixtures with a urine matrix. The concentration ranges considered are 1.56-10.92 and 25-100 micrograms/ml for the codeine-ephedrine mixture, and 0.8-3.2, 0.1-0.5 and 1.6-4.8 micrograms/ml for the acetylsalicylic acid-codeine-ephedrine mixture. The analytical results were quite good in all cases.

Calibration↗
PubMed1996

The reliability and significance of analytical data on the natural occurrence of fumonisins in food.

Several methods are presently used to identify and quantify fumonisins in foods and feeds. HPLC procedures on derivatized fumonisins with fluorescence detection are most commonly used. The validity and significance of reported fumonisin levels depend on several factors such as the specificity, detection limit, accuracy and reproducibility of the analytical method as well as on the sampling procedure used, and the integrity and purity of the analytical standards. The importance of these factors is discussed and the results of two international collaborative studies are presented on the determination of fumonisins in corn by a reversed-phase HPLC method on o-phthaldialdehyde (OPA) derivatized fumonisins using fluorescence detection.

Carcinogens, Environmental↗
PubMed1984

Data analytic methods for matched case-control studies.

The recent introduction of complex multivariate statistical models in matched case-control studies is a mixed blessing. Their use can lead to a better understanding of the way in which many variables contribute to the risk of disease. On the other hand, these powerful methods can obscure salient features in the data that might have been detected by other, less sophisticated methods. This shortcoming is due to a lack of support methodology for the routine use of these models. Satisfactory computation of estimated relative risks and their standard errors is not sufficient justification for the fitted model. Goodness of fit must be examined if inferences are to be trusted. This paper is concerned with the analysis of matched case-control studies with logistic models. Analogies of these models to linear regression models are emphasized. In particular, basic concepts such as analysis of variance, multiple correlation coefficient, one-degree-of-freedom tests, and residual analysis are discussed. The fairly new field of regression diagnostics is also introduced. All procedures are illustrated on a study of bladder cancer in males.

Analysis of Variance↗
PubMedDate not supplied

[The epidemiology of multiples sclerosis in Alcoi. Analytical data].

INTRODUCTION: The epidemiology of multiple sclerosis (ME) in the Alcoi area has been studied by our groups for many years. When studying the factors linked to ME in this area initially we observed that migration, contact with dogs and the textile industry were associated with the disorder. A later study, in which the migration factor was controlled, still showed a significant association with contact with dogs and the textile industry. OBJECTIVE: To make an analytical study avoiding the possible confusing effect of contact with the textile industry, since this may be associated with other factors. We also compared the results of previous studies. PATIENTS AND METHODS: We made a case control study in which each case was paired with four controls for age, sex and having worked or not worked in the textile industry. The cases fulfilled the criteria for diagnosis of ME. The control patients came from the Emergency and Trauma Departments of Alcoi hospital. RESULTS. We analyzed 37 patients and 148 controls. Significant values were obtained for smoking, low social class, chickenpox and measles infections when aged under 15 years, pneumonia when aged over 15 years and contact with dogs, sheep and dissolvents. CONCLUSIONS: Contact with dogs was associated with multiple sclerosis in all the studies carried out in the Alcoi area to date. This is therefore a risk factor for the disorder in the Alcoi population.

Adult↗
PubMed1985

Retrieval of analytical data and substance identification in systematic toxicological analysis by the mean list length approach.

Chromatographic techniques are basic tools in systematic toxicological analysis. Extensive data bases with retention parameters of known drugs to aid in the identification of substances found are available or in preparation. For a search in such a data base the computer is indispenable. The commonly used window search has some disadvantages which can be overcome by a search based on the statistical concept, the mean list length. The latter retrieval system gives for each candidate in the identification process a probability value. It is shown that these probability values are highly influenced by the reproducibility of the retention parameters of the analytical systems used. Explanations for these phenomena are given.

Chromatography, Gas↗
PubMed2004

Study of spectral analytical data using fingerprints and scaled similarity measurements.

A new chemoinformatic model has been developed for enlarging the differences between spectra and applied to differentiation of wines according to the criteria grape origin and variety and ageing process. The model is based on generation of fingerprints from normalised spectra, using empirical parameters and a set of 120 samples. After generation of the fingerprints, similarity matrixes were built on the basis of the Tanimoto similarity index between the fingerprints of the samples. Calculation of the Tanimoto index was modified to adapt the index to the characteristics of the analytical measurements. Thus, scaling factors taking into account pattern fingerprints generated from a group of samples with common characteristics were used. In addition, a modified expression for calculating the Tanimoto index was employed. Principal-components analysis (PCA) and soft independent modelling of class analogy (SIMCA) were applied to the similarity matrixes. The results obtained are discussed as a function of the normalisation method employed, the empirical factor used in generation of the fingerprints, and selection of samples for building the pattern fingerprint, etc. Finally, results from differentiation of wines are compared with those obtained by applying PCA to the unprocessed spectra as stated by the proposed model.

Journal Article↗
PubMed2001

Reliability and accuracy of environmental analytical data on moss samples: an interlaboratory comparison.

An inter-comparison exercise was performed between two laboratories on mineralised moss samples. Ten samples, together with three certified reference materials (CRM 61, CRM 62 and CRM 482) and five blanks were mineralised independently in the two laboratories and then analysed by both with different techniques (AAS, ICP-MS, and INAA). The elements analysed were: Cd, Cr, Cu, Fe, Ni, and Pb. Accuracy tests showed that, for AAS, the relative standard deviations for five repetitions of the same sample were between 0.2% for Cd and 2.9 % for Cr and that the concentration values found reference materials were withn one standard deviation from the certified values, with the exception of Cr and Cd for CRM 482. The statistical analysis was performed first with a simple linear regression and a Student t-test taking into account the possible influence of the mineralisation procedure and of the analytical technique, in order to evaluate their reliability. The results showed that more than 78% of the regressions had a correlation coefficient higher than 0.750, and that 83% of the slopes were not different from one with a level of significance of 0.01. Afterwards, the precision of the measurements were evaluated using maximum likelihood; the normalised errors showed that ICP-MS had a better performance on most of the elements analysed (with the exception of Fe) and that both the mineralisation procedures gave satisfactory results. The two laboratories were then found to produce reliable results.

Bryopsida↗
PubMedDate not supplied

A data-analytic approach for estimating lead time and screening benefit based on survival curves in randomized cancer screening trials.

Screening tests are used frequently for control of diseases such as cancer. The increased survival time of screen-detected cases over those that are detected clinically may be due in part to 'lead time', or the length of time by which the disease is diagnosed earlier by screening in the presence or absence of any real extension in survival time. A realistic evaluation of screening needs to assess the true benefit of screening; that is, the length of time by which survival has been extended, beyond merely the time of the advanced diagnosis. The comparison of survival measured from time of entry between cases in a screening arm and in a control arm in randomized studies avoids the lead time bias. If the effects of average lead time and average benefit on survival are additive, these effects can be estimated by recognizing that (a) the difference in survival curves since time of diagnosis confounds benefit and lead time, but (b) the difference in survival curves since time of start of study involves benefit only. The method is evaluated on simulated data for its accuracy and may be used on data from randomized studies.

Bias↗
PubMed1993

Combining independent studies of a diagnostic test into a summary ROC curve: data-analytic approaches and some additional considerations.

We consider how to combine several independent studies of the same diagnostic test, where each study reports an estimated false positive rate (FPR) and an estimated true positive rate (TPR). We propose constructing a summary receiver operating characteristic (ROC) curve by the following steps. (i) Convert each FPR to its logistic transform U and each TPR to its logistic transform V after increasing each observed frequency by adding 1/2. (ii) For each study calculate D = V - U, which is the log odds ratio of TPR and FPR, and S = V + U, an implied function of test threshold; then plot each study's point (Si, Di). (iii) Fit a robust-resistant regression line to these points (or an equally weighted least-squares regression line), with V - U as the dependent variable. (iv) Back-transform the line to ROC space. To avoid model-dependent extrapolation from irrelevant regions of ROC space we propose defining a priori a value of FPR so large that the test simply would not be used at that FPR, and a value of TPR so low that the test would not be used at that TPR. Then (a) only data points lying in the thus defined north-west rectangle of the unit square are used in the data analysis, and (b) the estimated summary ROC is depicted only within that subregion of the unit square. We illustrate the methods using simulated and real data sets, and we point to ways of comparing different tests and of taking into account the effects of covariates.

Carcinoma, Non-Small-Cell Lung↗
PubMed1988

Some normative, reliability, and factor analytic data for the revised UCLA Loneliness Scale.

Normative statistics are provided for the UCLA Loneliness Scale based on the results of a sample of 978 adult subjects collected during a general population health survey. Factor analysis of the data revealed that the scale had a two factor structure; positively worded items loaded on one factor and negatively worded items on the other. Results from the factor analysis were used to construct two equivalent 10-item short forms of the scale. Previous findings that the scale is highly reliable were confirmed.

Adolescent↗
PubMed1997

[Effectiveness and cost of 5-HT3-antagonists in acute chemotherapy-induced emesis. Health-economic analysis based on current meta-analytic data].

BACKGROUND: Cost containment measures in hospitals suspect the efficiency of 5-HT3-receptor antagonists (5-HT3-RA) in treating chemotherapy-induced emesis. RESEARCH: This paper compares the cost-efficacy of acute antiemetic interventions both for high and moderate emetogenic cancer treatments. The cost-efficacy-analysis is based on a recent metaanalysis comparing metoclopramide (MCP)- and 5-HT3-RA-containing antiemetic regimens both in comedication with corticosteroids. Total costs for treating moderate emetogenic cancer treatments sum up to DM 53.- for MCP-regimens and DM 55.- for 5-HT3-RA resp. In high emetogenic cancer treatments total costs for MCP-regimens are DM 76.- and DM 61.- for 5-HT3-RA. Total costs for fully controlled patients in moderate emetogenic cancer treatments are DM 77.- for MCP and DM 71.- for 5-HT3-RA. In high emetogenic cancer treatments costs for the fully controlled patient with MCP-regimens are DM 126.- and DM 79.- with 5-HT3-RA. CONCLUSION: Even under mere economical considerations 5-HT3-RAs should be prescribed in treating acute chemotherapy-induced emesis.

Antiemetics↗
PubMed1999

Orphenadrine poisoning in a child: clinical and analytical data.

Orphenadrine is an anticholinergic drug used mainly in the treatment of Parkinson's disease. It has a peripheral and central effect and a known cardiotoxic effect when taken in large doses. We report the successful outcome of the treatment of a 2 1/2-year-old girl who accidentally ingested 400 mg of orphenadrine hydrochloride (Disipal). One hour after ingestion she presented neurological symptoms: confusion, ataxic walking, and periods of severe agitation. Generalized tonic-clonic seizures appeared resistant to the administration of multiple antiepileptics. They ceased after a supplementary dose of intravenous diazepam, endotracheal intubation, and mechanical ventilation. An episode of ventricular tachycardia responded well to i. v. lidocaine. Physostigmine was administered in three successive doses. The initial orphenadrine plasma level (3,55 microg/ml) was in the toxic range, associated with high mortality. The calculated elimination half-life was 10.2 h and the molecule and/or its metabolites were found up to 90 h after ingestion.

Akathisia, Drug-Induced↗